Final answer:
In hydroelectric plants, water flows into the plant through a penstock, which is a pipeline that carries water to run turbines that generate electricity.
Step-by-step explanation:
In hydroelectric plants, water flows into the plant through the penstock. The penstock is a pipe or pressurized pipeline that transports water to the turbines inside the plant. The flowing water is instrumental in spinning the turbine blades, which subsequently rotate a connected generator to produce electricity. This process efficiently transforms the potential energy of the stored water behind a dam into kinetic energy and finally into electric power. Hydroelectric power is considered a sustainable and clean energy source since it does not produce direct emissions of air pollutants and relies on a continuously renewable resource.